Beneficiation of tin ore



Nov. 22, 1966 V. MERCADE ETAL BENEFICIATION 0F TIN ORE Filed Ma rch 20, 1964 ORE CRUSHING TO -20 MESH WET SCREENING 65 MESH +65 MESH WATE R I ROD MILLING -65 MESH SETTL I NG AND DECANTATION QULFIDE FP ----SULFIDE F -HYDROFLUORIC ACID XANTHATE LOTATION (2 STAGES) SULFIDE MD SLIMES --SULFIDE MD DESLIMING HYDROFLUORIC ACID,FATTY ACID ALKANOLAMIDE OR FATTY AMINE (WITHOUT FATTY ACID) SILICATE FP -----SIL|CATE FLOTATION 2 STAGES) SILICATE MD WASHINGS SILICATE MD WASHING CONTAINING FLUORIDE FATTY ACID ALKANOLAMIDE V AND FATTY ACID CASSITERITE FLOTATION STAGE I FLO AT (RECIRCULATION) INVENTORS VENANCIO MERCADE JAMES B. DUKE ATTORNEY United States Patent 3,286,837 BENEFICIATION 0F TIN ORE Venancio Mercade and James B. Duke, Metuchen, NJ.,

assignors to Minerals & Chemicals 'Philipp Corporation, Township of Woodbridge, NJ., a corporation of Maryland Filed Mar. 20, 1964, Ser. No. 353,559 15 Claims. (Cl. 209-166) This invention relates generally to the beneficiation of tin ore and relates especially to a flotation process for recovering an exceptionally high grade cassiterite concentrate from low grade cassiterite ore.

Tin is presently obtained from low grade vein tin ores in Bolivia. From a metallurgical point of view the ores consist essentially of quartz, tourmaline, feldspar, micas, iron oxides, a variety of sulfides (of which iron sulfide predominates) and small amounts of cassiterite which con stitute the only valuable mineral in the ore. Of the nonsulfide gangue minerals quartz and silicate minerals (especially feldspar and micas) usually predominate. A typical Bolivian ore may contain only about /2 to 2% cassiterite (SnO the balance being sulfides, quartz and silicates. At present these tin ores are concentrated by gravimetric processes, such as the procedure described in an article by O. M. Davila in Engineering and Mining Journal, vol. 158, No. 11 pages 100-108, entitled, How Empresa Minera de Catavi Concentrates Tin Ores. The process involves a heavy media concentration of coarsely crushed low grade tin ores, followed by jigging and table concentration to produce a cassiterite concentrate which is subjected to froth flotation with a xanthate collector reagent to float sulfide from the cassiterite. By this procedure, a material assaying about 55% Sn is obtained from the low grade ore. This grade represents a concentrate of about 70% purity (expressed as SnO The recovery of cassiterite is reported to be in the neighborhood of only 40% to 50% as a result of losses in the gravimetric concentration steps.

Many attempts have been made to float cassiterite from tin ores, especially high grade tin ores, and a variety of collector reagents has been suggested. Among the collector reagents that have been employed on an experimental basis may be mentioned quaternary ammonium compounds, alkyl cetyl sulfate, oleic acid and sodium oleate. The results, however, have not been sufficiently satisfactory with low grade tin ores, such as those ores found in Bolivia and in South Africa, because of the failure to develop reagents of adequate selectivity for the cassiterite. To the best of our knowledge, cassiterite is not floated commercially from any tin ores, even from high grade placer ores which would be expected to be more responsive to beneficiation by flotation than low grade ores.

A noteworthy advance in the art of tin ore beneficiation has been the recent discovery that the combination of a fatty acid, especially lauric acid, with a water-dispersible fatty acid alkanolamide is exceptionally effective in concentrating cassiterite in an acid flotation pulp. The use of such combination of flotation reagents as a collector reagent for cassiterite is disclosed and claimed in a copending application of James B. Duke, Serial No, 181,- 093, filed March 20, 1962, now US. 3,182,798. In applying this discovery to the concentration of cassiterite from low grade ore, such as Bolivian tin ore, the ore may be initially tabled and/ or subjected to a bulk sulfide flotation. Hydrofluoric acid is used to depress cassiterite and quartz during the sulfide float. The tailing of the flotation step, which is a rough concentrate of cassiterite, silicate minerals (especially feldspars, micas, beryl, topaz and tourmaline) and large quantities of quartz, is deslimed and then conditioned for flotation of cassiterite with the combination of lauric acid and fatty acid alkanolamide re- 3,286,837 Patented Nov. 22, 1966 agents in an acid pulp. The overall recovery of cassiterite obtained in this manner has compared favorably with recoveries in commercial gravimetric processes. The grade of tin concentrate obtained by such flotation process leaves something to be desired since it is usually not appreciably greater than the typical 55% Sn grade of concentrates obtained in the commercial process with a sink-float step and without a cassiterite flotation step. The reason for this is that the cassiterite concentrate obtained with the cooperative collector reagents contains oxidized gangue minerals which have flotation characteristics generally similar to cassiterite. These minerals, principally silicate minerals, are therefore floated with the lauric acid and alkanolamide cooperative collector reagents and report in the froth concentrate along with the cassiterite. The same problem exists when other collector reagents for cassiterite are used.

Accordingly, an object of this invention is the provision of a method for improving substantially the grade of cassiterite concentrate that can be obtained by flotation of cassiterite from nonsulfide gangue.

A more specific object of this invention is the provision of a method for increasing substantially the grade of cassiterite concentrate that can be produced when cassiterite is floated from nonsulfide gangue with the combination of fatty acid and fatty acid alkanolamide cooperative collector reagents.

Still another object of the invention is to provide for the initial selective flotation of silicate minerals having flotation characteristics similar to cassiterite before floating the cassiterite, thereby to improve the selectivity of the combination of lauric acid and fatty acid alkanolamide reagents for cassiterite.

Stated in another manner, an object of this invention is the provision of a method for improving the grade of cassiterite obtainable by flotation with fatty acid and fatty acid alkanolamide as cooperative collector reagents in an acid pulp.

A specific object is the provision of a method for producing tin concentrates of purity or more from low grade ores containing only about 1% to 2% tin.

Another object is the provision of a process for floating cassiterite from nonsulfide gangue with reagents that are so selective to cassiterite that the process is even applicable to the beneficiation of slimed pulps obtained when the tailings of the sulfide flotation are deslimed prior to flotation for recovery of cassiterite.

This invention stems from the discovery of an exceptionally effective method for removing nonsulfide gangue minerals which have flotation characteristics similar to cassiterite from a tin ore, whereby cassiterite concentrates of exceptionally high purity can be subsequently recovered from a pulp of the tin ore.

Briefly stated, in accordance with this invention, oxidized gangue minerals (especially silicate minerals) that have flotation characteristics similar to cassiterite are selectively removed from a pulp of the ore after bulk flotation of sulfide minerals that may be present in the ore but before flotation of the cassiterite. This result is realized by conditioning an aqueous pulp of the ore with fluoride ion and with cationic nitrogenous collector reagent, without addition of an anionic (e.g., fatty acid) cooperative reagent. The conditioned pulp is subjected to froth flotation in an acid flotation circuit, producing a silicate-rich froth product which is discarded and a machine discharge product which is washed in a manner such as to remove fluoride ion and, preferably, to remove slime. The washings are discarded, thereby providing an aqueous pulp from which cassiterite is concentrated by froth flotation, preferably using the combination of a fatty acid, especially lauric acid, and a cationic collector reagent, especially a fatty acid alkonolamide, in an acid flotation circuit. pends upon the phenomenon that cassiterite is depressed when flotation is carried out with hydrofluoric acid and cationic collector reagent in the absence of higher fatty acid reagent but is especially amenable to flotation in an acid circuit with the combination of a cationic reagent and fatty acid in the absence of hydrofluoric acid.

Most tin ores, especially low grade vein ores, also contain sulfide minerals. In this case, the ore, previously tabled if the nature of the ore indicates such pretreatment, is initially conditioned for sulfide flotation with a xanthate collector and with fluoride ion to depress cassiterite and quartz. The machine discharge of the sulfide flotation step, preferably after an initial desliming, is treated for flotation of silicate minerals and then for cassiterite flotation, as described hereinabove. Substantially all residual sulfide minerals in the pulp after the bulk sulfide float will report in the froth product of the silicate flotation step. As a result, the silicate flotation step prevents contamination of the cassiterite concentrate with sulfide and silicate minerals which would normally report in the cassiterite concentrate.

A unique characteristic of our process resides in the fact that only a portion of the silicate minerals that are removed from the cassiterite by flotation report in the froth product; the remainder of these silicate minerals report in the machine discharge product along with the cassiterite. The latter silicates, which are slimed minerals, are removed from the cassiterite when the machine discharge product is washed to remove fluoride ions before the cassiterite flotation is carried out.

In accordance with a presently preferred form of the subject invention, an aqueous acidic pulp of cassiterite containing oxidized gangue minerals including silicate minerals, especially feldspars and quartz, is prepared for the initial selective flotation of silicate minerals from the cassiterite and quartz with fluoride ion and nitrogenous collector reagent (fatty acid amine or fatty acid alkanolamide) in the absence of fatty acid. The pulp is then subjected to froth flotation, as described above. The flotation tailing, which is a rough cassiterite concentrate, is washed to remove fluoride ion and any adherent silicate gangue and then conditioned for selective froth flotation of cassiterite from residual gangue (principally quartz) with the combination of fatty acid alkanolamide and lauric acid. The conditioned pulp is subjected to froth flotation in an acid pulp, producing a froth product which is a high grade cassiterite concentrate.

It is also fully within the scope of this invention to subject the machine discharge product of sulfide flotation to successive silicate and cassiterite flotation without a preliminary desliming step since the reagents employed in the flotation steps have excellent selectivity even in the presence of grinding slimes. However, the grade of cassiterite concentrate will usually be lower than the grade of cassiterite obtained by floating a deslimed feed.

Cassiterite concentrate of exceptional purity have been obtained from very low grade tin ores by flotation with the combination of fatty acid alkanolamide and lauric acid reagents when silicate minerals and any residual sulfide minerals are initially floated from cassiterite and gangue in the pulp, in accordance with the subject invention. By way of example, flotation concentrates of 75% to 90% purity. have been obtained at satisfactory weight recoveries from a low grade Bolivian ore containing only about 1% tin (as SnO when silicates were selectively floated from a deslimed pulp with fluoride ion and fatty acid alkanolamide after sulfide flotation and before cassiterite flotation with the combination of fatty acid alkanolamide and lauric acid. Similar results were obtained when a fatty amine salt was substituted for the fatty acid alkanolamide in the silicate flotation step, but

not in the cassiterite flotation. In the absence of a silicate flotation step, concentrates having a comparatively low grade of about 60% SnO are obtained from the same The operativeness of the process deore by the present commercial process. In effect, the purity of tin concentrates can be increased by 15% to 30% by practicing the present invention. As another example, a slimed concentrate of about 60% SnO grade, representing about 9% of the tin values in a low grade Bolivian ore, was reclaimed from slimes obtained by by draulic washings of a sulfide machine discharge product. It was found that a composite of about 83% purity could be produced at an excellent weight recovery of about 61% by combining this 60% Sn0 grade slimed concentrate with a concentrate obtained by treating a deslimed sulfide machine discharge product to silicate flotation and then to cassiterite flotation, in accordance with this invention.

This invention will be more fully understood by the following description, taken in connection with the accompanying drawing, which is a flow sheet of a typical plant for concentrating cassiterite from a complex ore containing sulfiide, quartz and silicate gangue minerals, in accordance with this invention.

PREPARATION OF ORE The mill heads are crushed to about 20 mesh and then ground to minus 65 mesh in a rod mill. The ground pulp is thickened by sedimentation before sulfide flotation.

SULFIDE FLOTATION The thickened feed is subjected to a sulfide flotation with the usual xanthate collector reagents. Present results indicate that it is highly advantageous to incorporate fluoride ion into the pulp before reagentizing the pulp with xanthate and to carry out the sulfide flotation operation in an acid circuit. A pH of 3 to 5 is suitable. About 1 to 10 pounds of hydrofluoric acid per ton of dry feed can be used. Any of the usual xanthate collector reagents can be employed as the selective sulfide collector, as examples of which may be mentioned potassium ethyl xanthate, potassium n-hexyl xanthate, sodium ethyl xanthate, sodium isopropyl xanthate and sodium sec-butyl xanthate. The details of the sulfide flotation step will obviously vary with the nature of the sulfide minerals present in the tin ore and can be readily determined by applying the usual considerations that are familiar to those skilled in the art. The conditioned pulp is aerated in any suitable flotation machine, removing a sulfide float and a machine discharge product which is a concentrate of cassiterite together with oxidized gangue minerals.

The machine discharge product of the sulfide flotation step is preferably deslimed, as by washing and decantation, to remove minus 325 mesh slimes. These slimes can be concentrated for recovery of cassiterite by thickening the slimes and subjecting the slimes to silicate flotation with hydrofluoric acid and cationic nitrogenous collector without fatty acid and then to cassiterite flotation with fatty acid alkanolamide together. with fatty acid.

SILICATE FLOTATION Hydrofluoric acid (or the combination of fluoride salt, such as sodium fluoride, and mineral acid, such as sulfuric to form hydrofluoric acid in situ) is then incorporated into an aqueous pulp of the sulfide flotation tailing. Agitation of the pulp with fluoride ion before incorporation of nitrogenous flotationreagent appears to be desirable. Excellent results have been realized when hydrofluoric acid was used in amount of about 10 pounds per ton of feed. The fluoride treated pulp is then conditioned for flotation with a cationic nitrogenous flotation reagent which can be a higher fatty amine or a hydrotropic fatty acid alkanolamide. While the latter class of reagents is sometimes referred to as being nonionic in character, this type of amide has cationic properties in acid pulps. Therefore, for purposes of describing this invention, the hydrotropic fatty acid alkanolamides are included in the class of cationic materials- In carrying out the silicate flotation step, any of the usual cationic nitrogenous collectors can be used with the fluoridated pulp. Stage addition of collector reagent is strongly recommended and residual sulfide minerals concentrate in the initial float product. About 2 to pounds of collector reagent is employed except in the treatment of slimes in which case appreciably smaller quantities of reagent can be used. Especially useful are n-primary fatty acid amines containing 18 carbon atoms. Since the preferred amines have poor solubility, they should be used as amine salts formed by addition to the amine of a water-soluble acid, such as acetic acid or bydrochloric acid. Especially recommended are salts of C Salts of C amines tend to collect cassiterite, as shown in US. 3,167,502 to James B. Duke. The use of a C amine salt in the silicate flotation step would therefore lead to a poor recovery of cassiterite in the process of the invention. The amine salts can be derived from natural fatty acid mixtures obtained, for example, from coconut oil, cottonseed oil, soybean oil or lard oils. Thus, for example, there may be used tallow amines (derived from tallow and in which tallow comprises a mixture of the following radicals: dodecyl, tetradecyl, tetradecenyl, hexadecyl, hexadecenyl, octadecyl, octadecenyl, octadecadienyl and eicosyl); cocoamine-s (derived from coconut oil and in which coco comprises a mixture of hexyl, octyl, decyl, dodecyl, tetradecyl, hexadecy-l, octadecyl, octadecenyl, and octadecadienyl radicals); and soya-amines (derived from soybean oil and in which soya comprises a mixture of hexadecyl, octadecyl, eicosyl, octadecenyl, octadecadienyl, and octadecatrienyl radicals).

Hydrotropic fatty acid alkanolamides employed in carrying out the silicate and/or cassiterite flotation step (hereinafter described) are described in SchWartz-Perrys Surface Active Agents, pages 212-213 (1949) and are produced by mixing 1 mol of fatty acid with 1 to 2 mols of alkanolamine and condensing the mixture at a temperature below the decomposition temperature of the resulting hydrotropic material. Diethanolamine is most frequently used in the process but other alkanolamines, such as rnonoethanolamine and isopropanolamine, can be used, as can mixtures of any of the aforementioned alkanolamines. The fatty acids commercially used in producing these amides are derived from naturally occurring animal and vegetable oils and fats which are sometimes hydrogenated. As examples of suitable fatty acids can be mentioned stearic acid, oleic acid, palmitic acid, linoleic acid, lauric acid, myristic acid and coconut fatty acids. The coconut fatty acids are employed most frequently. Surface active alkanolamides used in carrying out this invention have the following structural formula:

0 RIOH ll RI C"'N wherein: R is selected from the group consisting of n-alkyl and n-alkenylgroups containing from 11 to 17 carbon atoms, R is an alkylene group containing from 2 to 3 carbon atoms and R is selected from the group consisting of hydrogen and alkanol groups having from 2 to 3 carbon atoms. Some species of hydrotropic fatty acid alkanolamides are coconut fatty acid diethanolamide, lauric acid diethanolamide, stearic acid monoethanolamide and oleic acid diethanolamide.

Flotation of silicate minerals, e.g., feldspar, topaz, tourmaline and beryl, is carried out in a highly acid circuit, such as at a pH of 2 to 4. Acid mine Water is suitable in making up the flotation pulp. The flotation tailing, which is a rough concentrate of cassiterite, is washed to remove fluoride ion substantially completely before the product is prepared for cassiterite flotation. The machine discharge product should also be deslimed during the washing step since an appreciable quantity of slimed silicate minerals will be removed in this manner. The slime cutoff can be at 325 mesh, for example.

CASSITERITE FLOTATION The washed and deslimed machine discharge product of the silicate flotation step is conditioned for cassiterite flotation with the combination of water-dispersible fatty acid alkanolamide and fatty acid, preferably lauric acid (or mixed fatty acid consisting predominately of lauric acid) Laurie acid appears to be markedly superior to other fatty acids, such as oleic acid. Alkanolamide can be employed in amount of about /2 to 5, and preferably 1 to 2, pounds per ton of dry feed (i.e., dry machine discharge of the sulfide flotation.) Fatty acid can be used in amount of about 1 to 10 pounds and preferably about 4 /2 to 9 pounds per ton of the feed. The conditioning agents are preferably incorporated by stage addition.

The feed to cassiterite flotation is passed to the flotation cells and subjected to froth flotation in an acid circuit, typically at a pH of 2 to 4, withdrawing a froth product which is a concentrate of cassiterite. The froth is normally cleaned one or more times to improve product grade. Recovery of cassiterite can be improved by recirculating middlings. The tailing of the cassiterite flotation consists for the most part of quartz.

The following examples illustrate the concentration of cassiterite from low grade tin ores containing sulfide and silicate gangue minerals.

All mesh sizes mentioned in the examples refer to values obtained with Tyler Screen-scale Sieves. The term MD refers to machine discharge product and PP refers to froth product. Mids refers to middlings.

Reagents referred to in the examples are identified as follows:

Monamid=Monamid J50CE, 1:1 coconut fatty acid diethanolamide obtained by condensing 1 mol coconut fatty acid with 1 mol diethanolamine. Reported to analyze 86% condensate, 3.5% uncondensed fatty acid (as lauric). Alkali No. (mg. KOH/gm.)=4050.

M0namine=M0namine ADD-100, 2:1 coconut fatty acid diethanolamide obtained by condensing 1 mol coconut fatty acid with 2 mols diethanolamine.

Armac 12=dodecylamine acetate.

Armac 18=octadecylamine acetate.

CT 0=crude tall oil.

Neo Fat 265=mixture of fatty acids in proportion of 93% saturated and 7% unsaturated. Main constituents are 52% lauric acid and 19% myristic acid.

Neo Fat 140=mixture of fatty acids in proportion of 95% unsaturated and 5% saturated. Main constituents are 59% linoleic acid and 34% oleic acid.

Z-9 Xanthate=potassium isopropyl xanthate.

Example I This example illustrates the beneficiation of a South African tin ore by the process of this invention. The ore was a low grade ore and contained a substantial percentage of tin values in the minus 10 micron particle size range.

In this example, all water used in processing the ore, ncluding Water used in grinding, washing and condition- 1ng, was tap water that had been acidified to a pH of 3.0 with sulfuric acid.

Five hundred grams of the ore was crushed to percent minus 20 mesh and the minus 20 mesh ore was wet screened through a 65 mesh screen. The plus 65 mesh portion was wet ground to minus 65 mesh by 3 minutes rod milling at 60% solids. All of the minus 65 mesh ore was combined and washed to remove soluble salts by diluting the ore with the acidified Water, settling and decantation. The ore was subjected to a two-stage sulfide flotation, the details of which are summarized below. Sulfide conditioning and flotations were in 500 gram froth flotation cells. The machine discharge product of the sulfide flotation step was deslimed at 325 mesh. The deslimed sulfide 7. machine discharge product was conditioned for two-stage silicate flotation with hydrofluoric acid and fatty acid alkanolamide, in accordance with this invention. The details of conditioning and flotation are summarized in table form. Conditioning for the first silicate float was in a 250 gram flotation cell. The other silicate conditioning and flotations were in a 500 gram flotation cell.v The machine discharge product was diluted with the acidified water and passed through a 325 mesh screen. This procedure was repeated two more times so as to wash thoroughly the silicate machine discharge product. The washed silicate machine discharge product was conditioned for cassiterite flotation with fatty acid alkanolamide and then fatty acid and subjected to a three-stage cassiterite floatation. Conditioning for the first cassiterite flotation was in a 250 gram flotation cell and all other cassiterite conditioning and flotation operations were in 500 gram cells. The froth products of the three cassiterite flotations were combined and the resulting rougher concentrate was cleaned six times. In the first cleaning operation the froth product was subjected to flotation for 3 minutes in a 500 gram froth flotation cell. The second cleaning was carried out by subjecting the froth product from the first cleaning to flotation for 2 minutes in a 250 gram froth flotation cell. The third, fourth, fifth and sixth cleanings were each carried out in the same manner as the second cleaning. The cleaned froth product, which was the tin concentrate, was dried and divided into magnetic and nonmagnetic portions using a hand magnet. Following are the details of the beneficiation treatment.

CONCENTRATION OF CASSITERITE- SOUTH AFRICAN ORE Condi- Float Reagents Amount Lbs/ton tioning Time,

Time, min.

min.

SULFIDE FLOTATION-STAGE 1 HF 50 ml. as 5% aq. so1n 10. H 804 25 ml. as 5% aq. soln- 5. 0 Z-9 Xanthate- 20 m. as 2.5% aq. so1n 2. 0 Pine Oil 10 drops 0.3 3

Solids In Conditioning and Flotation=25% STAGE 2 Z-9 Xanthate 10 ml. as 2.5% aq. soln i 1. 0 1 2 Solids In Conditioning and Flotation, About 25% SILICATE FLOTATIONSTAGE 1 HF 25 ml. as 5% aq. soln 5. 0 Monamid 0.31 2 3 6.3 ml. as 1.25% aq. soln Solids In Conditioning=25% Solids In Flotation=% STAGE 2 25 as 5% aq. soln 5. 0 12.6 ml. as 1.25% aq. Solo. 0. 62 1 h Solids In Conditioning and Flotation, About 15% CASSITERITE FLOTATIONSTAGE 1 Monarnid 12.6 1111. as 1.25% aq. soln 0.62 1

Neo Fat 265--- 85 drops 2.66 5 3 Solids In Conditioning, -22% Solids In Flotation, About 12-14% 5 3 Solids In Conditioning and Flotation, About 12-14% Metallurgical results for the beneficiation of the South Africa tin ore are given in Table I.

TABLE I.FLOIATION METALLURGICAL RESULTSSOUTH AFRICAN ORE Products Percent Percent Percent Sn W Sn Distribution Tin cone. (nonmagnetic) 1.42 49.38 32.8

Tin cone (magnetic). 0. 37 0. 0. 1

Tm mid-6 0. 09 16. 72 0. 7

Tin mids 5-4-3. 0. 84 11. 10 4. 4

Tin mids 2-1 5. 36 5. 11 12. 8

Sulfide FP 10. 42 1. 28. 6. 2

Head 100. 00 1 2. 13 100. 0

Conc.+mid-6 1. 51 1 47. 42 33. 5

Conc.+mids 6-54-3 2. 35 1 34. 43 37. 9

Conc.+mids 65-43-21 7. 71 1 14. 05 50. 7

Feed to cassiterite flotation 58. 59 1 2 38 65.2 Calculated recovery based on recirculation of the middlings during cassiterite flotation. 75. 3

1 Calculated values.

Data in Table I show that a nonmagnetic tin concentrate of 49.38% Sn grade was obtained at a 32.8% recovery from the 2.13% Sn grade South African ore by the process of this invention. Assuming recirculation of middlings during cassiterite flotation, the data indicate that recovery could have been increased to 75.3

Data in Table I for the silicate flotation step indicate that the silicate flotation reagents were highly selective for silicate minerals and that there was only a small loss of tin in the silicate froth product.

The following examples illustrate the concentration of cassiterite from a low grade ore obtained from Empresa Minera de Catavi in Bolivia. The ore assayed 1.23% Sn, principally as cassiterite, representing 1.56% SnO It is reported that the ore :also contained cylindrite, stannite, pyrite, marcasite, pyrrhotite, antimonite, bismuthinite, sphalerite, galcna, silver sulfides, chalcopyrite, tourmaline, limonite, hematite, feldspar, sericite, topaz, mica, fluorite and relatively large quantities of quartz.

Example I] t In preparing the ore for flotation, 500 grams of a representative sample of the Bolivian ore was chushed to minus 20 mesh, wet screened through a 65 mesh screen and the plus 65 mesh fraction ground to minus 65 mesh by 3 minute rod milling at 60% solids. Supernat-ant liquid was siphoned off after a 30 minute settling time :and discarded. All of the minus 65 mesh fractions were combined and used in flotation tests.

The ground ore was subjected to two-stage sulfide, flotation. The sulfide machine discharge was deslirned at 325 mesh and subjected to a two-stage silicate flotation in an acid circuit with hydrofluoric acid and alkanolamide reagents. The machine discharge product of silicate flotation was thoroughly washed to remove fluoride ion (and simultaneously deslimed). The deslimed product was subjected to cassiterite floation with lauric acid and .alkanolamide reagents in three stages and the combined froth products of these three stages were given five cleanings. In the process, tap Water adjusted to a pH of 3.0 with H 50 was used throughout screening, grinding and flotation. The percentsolids in the conditioning and flotation steps was substantially the same as in Example I.

Flotation reagents and conditions used in the three flotation steps are summarized below. In this summary, reagents are listed in the order in which they were incorporated into the pulp. A dash under the column entitled Conditioning Time indicates that the pulp was not conditioned after addition of the reagent indicated. For example, in the first-stage silicate flotation step the pulp was not conditioned after addition of the acid but was conditioned for 1 minute after subsequent addition of alkanolamide to the pulp already containing the acid.

CONCENTRATION OF CASSITERITE- BOLIVIAN ORE Reagent Condition- Float Time, Reagents Quantity, ing Time, min.

lbs/ton min.

SULFIDE FLOTATIONSTA GE 1 10.0 5. 2. 0 Pine Oil 0. 3

STAGE 2 Z-Q Xanthate 1. 0 1 2 SILICATE FLOTATIONSTA GE 1 5.0 Monamid 150-OE 0. 25 2 5 STAGE 2 HF 5. 0 Monamid 150-CE 0. 50 1 8 CASSITERITE FLOTATION-STAGE 1 Monamid ISO-OE 1. 0 1 Neo Fat 265 2. 2' 5 3 STAGE 2 Neo Fat 265 1. 125 5 3 STAGE 3 Neo Fat 265 1. 125 5 3 Metallurgical results are reported in Table II.

TABLE II.FLOTATION METALLURGICAL RESULTS- BOLIVIAN ORE 1 Calculated.

Results in Table II show that 37.8% of the tin in the original ore was recovered in the form of a high grade concentrate analyzing 66.07% Sn by combined sulfide silicate and cassiterite flotations, in accordance with the present invention. The 66.07% Sn grade of the concentrate corresponds to a purity of about 84%, as compared with the approximate 60% to 70% purity obtained with current practice. Data in Table II indicate also that 57.7% of the cassiterite in the feed to cassiterite flotation cells was recovered in the tin concentrate product.

The data show also that after removal of sulfides and silicates, and on the basis of a deslimed feed to cassiterite flotation, the recovery obtained by recirculating the middlings is 83.5%. This value is calculated from the following equation. In the equation c represents percent Sn in the concentrate; f represents percent Sn in the head of cassiterite flotation; t represents percent Sn in the cassiterite flotation tailing.

Example III Summarized metallurgical data for variations of reagents in the process of Example III are reported in Table III. In Table III, Tests No. 1, and 3 through 7, inclusive, represent examples of the process of the subject invention. (Test No. 1 corresponds to Example II.) Of these, Tests No. 1 through 6 were carried out on a deslimed sulfide machine discharge product obtained by flotation as described in Example II. Test No. 7 was carried out on a sulfide machine discharge product which had not been deslimed. Tests No. 1 through 7 embrace the use of four diflerent cationic nitrogenous collector reagents in the silicate flotation step. In Test No. 2 the cationic nitrogenous reagent was a C fatty amine, the use of which is outside the scope of this invention. This reagent was also used in Test No. 8 during the silicate flotation step. Tests No. 8 through 11, inclusive, represent experiments in which the fatty acid cooperative reagents for cassiterite flotation were outside the scope of the present invention. Similarly, Test No. 12 represents an experiment in which the fatty acid cooperative reagent was used in combination with a cationic reagent outside the scope of this invention.

In all cases, stage addition of reagents was used and the general procedure of Example II was followed.

To simplify a comparison of the metallurgical results cone. head Recovery cone. max. head concentration efficiency In the case of cassiterite, conc. max.=78.8, corresponding to the Sn0 grade of a cassiterite concentrate of purity.

TABLE III.CONCENTRATION OF CASSITERITE FROM SULFIDE FLOTATION TAILING BY PRELIMINARY SILICATE FLOTATION FOLLOWED BY FLOIATION OF CASSITERITE I Silicate Flotation Silicate Froth Product Cassiterite Flotation Cassiterite Concentrate Test Percent Sn Percent Sn Concen- No. Dist. (calculated) tration Reagents Lbs/ton Percent Percent Percent Reagents Lbs/ton Percent Percent Head Etficiency Wt. Sn Sn Dist. Wt. Sn

Over- $1103 an 1 1 HF 10.0 4. 37 1. 65 1.0 0. 61 66. O7 37. 8 57. 7 1. 07 r 31. 6

Monamid- O. 75 4. 5

Armac 12 0. 15 4.

Armac 18- 0. 15 Neo Fat 265..- 4. 5

4 F 10. 0 6. 09 0.90 4. 5 Monamine. 1.0 0. 84 63.16 43. 7 67.9 1. 22 37. 5

Monamid 0. 75 Non Fat 265--. 4. 5

5 F 10. O 6. 86 0. 83 4. 9 Monamine. 1.0 0. 86 64. 04 47. 0 71. 6 1. 17 38. 1

Mona- 0. 75 Neo Fat 265 4. 5

mine.

6 HF 10. 0 4. 89 1. 35 6. 3 Monarnine- 1. 0 0. 80 60. 13 45. 3 70. 5 1. 06 34.4

Armac 18 0. 15 4. 5

Monamid- 0. 75 5. 63

Armac 12- 0. 15 1. 0 v

Monamid 0. 75 2. 25

Monamid- 0.75 Neo Fat 140.- 4. 5

11 10. 0 3. 80 1. 34 4. 8 MonamiCL 1. 0 0. 49 60. 45 27. 7 32.6 1. 07 21. 2

, Monamid 0. 75 Oleic Acid 4. 5

12 10. 0 3. 59 1. 59 4.6 Arm-ac 18- 0. 10 1. 54 37. 86 47. 2 72. 3 1. 24 22. 3

Armac 18- 0. 15 Nee Fat 265--- 2. 0

1 Recovery based on Sn content of starting ore. 2 Recovery based on Sn content of feed to cassiterite flotation step. 3 Undeslimed feed to silicate flotation.

Data in Table III for the silicate flotation'step show that silicate froth products analyzing appreciably less than 2% Sn and generally representing less than 7% of the tin values of deslimed sulfide flotation tailings were obtained by carrying out the flotation concentration of silicate minerals in the presence of hydrofluoric acid and fatty acid diethanolamide or C amine salt. In most 0 fthe tests carried out with the hydrofluoric acid and alkanolamides, the tin grade of the silicate froth was much less than that of the heads and less than 5% of the tin was lost in the froth. These data therefore indicate that the C amine salt and alkanolamides, especially the latter, were selective to silicate in the presence of hydrofluoric acid and in the absence of fatty acid. On the other hand, tests made with hydrofluoric acid and C amine salt in the absence of fatty acid (Tests No. 2 and 8) resulted in an undesirable concentration of tin, with froth products of 2.70% to 2.89% Sn grade and representing 14.7 to 20.7% of the tin values.

Metallurgical data in Table III for the cassiterite flotation step per se show that cassiterite concentrates of excellent 60.13% to 66.07% Sn grade could be obtained at recoveries exceeding 57% by floating the cassiterite from the washed silicate talings with the combination of a C fatty acid and fatty acid alkanolamide. Thus, in Tests No. 3 to 6, concentrates of 60.13 to 64.95% Sn grades were obtained at excellent tin recoveries of 67.9 to 71.6%. Since the silicate flotation tailings used as the flotation feed in producing the cassiterite concentrates in Tests No. 3 to 6 were obtained with reagents highly selective to the silicate minerals, overall cassiterite recovery in these tests was excellent. Thus, in Tests No. 3 to 6 the overall recovery of tin in the mill heads was 43.7 to 47.0%. In Test No. 1, overall recovery was somewhat poorer than in Tests N0. 3 to 6 (although grade was superior) because the tin loss in the silicate flotation step was rather large in this particular test. In Test No. 7 the pulp had not been deslimed before silicate flotation and the amount of cassiterite. floated was less than in Tests No. 3 to 6 in which the pulp was deslimed before cassiterite. flotation. However, using the undeslimed feed, the overall tin recovery was comparable to the results in Tests No. 3 to 6. Data for Tests No. 8 and HF Monamid 150-CE 12 show that product grade was extremely poor when amines (Armac 12 or Armac 18) were substituted for the alkanolamide reagent in the cassiterite flotation step. Data for Tests No. 9 through 11 shows that grade and/ or recovery were adversely affected when fatty acids other than lauric were used with the coconut fatty acid alkanolamide in cassiterite flotation.

The following examples illustrate the application of the process of this invention to the concentration of cassiterite from low grade tin slimes from the Bolivian ore.

Example IV.

Part A.--Minus 325 mesh sulfide machine discharge slimes from the flotation of the Catavi tin ore, as described in Example H, were settled for 3 hours and supernatant liquid was siphoned off. The residue was subjected to two-stage silicate flotation and the machine discharge product of the silicate flotation operation was thoroughly washed four times with a 30 minute settling and siphoning for each Washing. ,The washed machine dicharge was subjected to three-stage cassiterite flotation and the combined froth products of the cassiterite flotations were refloated twice. Tap water acidified with H SO to pH of 3.0 was used throughout flotation and in the washing step.

TIN SLIME FLOTATION-BOLIVIAN ORE Reagent Quantity, lbs/Ton Conditioning Float Time,

Reagents Time, Min. Min

SILICATE FLOTA'IION-STAGE 1 5. 0 0.25 2 Percent Solids In Condit.

HF Monamid -OE STAGE 2 13 TIN SLIME FLOTATIOIILBOLIVIAN ORE-Cont.

Reagent, Condi-tion- Float Time, Reagents Quantity, ing Time, Min.

lbs. Ton Min.

CASSITE RITE FLOTATIONSTAGE 1 Monamid neon 1. 1 Neo Fat 265-.. 2. 25 3 Percent Solids In Conditioner=6% STAGE 2 Neo Fat 265 l. 125 5 3 STAGE 3 Neo Fat 265 1. 125 5 3 TABLE IV.-METALLURGICAL RESULTS OF SLIME FLOTATION Products Percent Wt. Percent Sn Percent Sn Distribution 1 Calculated.

Part B.In Table V there are summarized metallurgical results of a series of flotation and dispersion tests on minus 325 grinding slimes obtained by desliming a machine discharge of a two-stage sulfide flotation of the Catavi tin ore. Test No. 16 in the table represents data for the experiment described in Part A of this example. In all flotation tests a two stage silicate float was made with the reagents mentioned in Table V and the machine discharge product of silicate flotation was washed as in this example, Part A. The washed machine discharge product was subjected to three-stage cassiterite flotation and the froth cleaned twice as in Part A of this example. Reagents used in cassiterite flotation step were Monamid ISO-CE, 1 lb./ton and Neo Fat 265, 4.5 lb./ton.

provement in recovery when the pulp was preconditioned with the hydrofluoric acid reagent.

We claim:

1. In a method for recovering ca ssiterite from an ore containing silicate and quartz minerals wherein the cassiterite is floated from gangue minerals in an acid pulp in the presence of collector reagents capable of floating both cassiterite and silicate gangue minerals,

a preliminary step of subjecting an aqueous pulp or the ore to flotation in an acid circuit in the presence of a cationic nitrogenous collector reagent and fluoride ion in the absence of a fatty acid reagent, said cationic nitrogenous collector reagent being selected from the group consisting of fatty amine containing '18 carbon atoms and fatty acid alkanolamide derived from fatty acids containing from 12 to 18 carbon atoms, thereby to produce a silicate-rich froth product and a machine discharge product, washing said machine discharge product until said machine discharge product is substantially free of fluoride ion, thereby providing an aqueous pulp that is more amenable to subsequent concentration of cassiterite by [froth flotation in an acid circuit in the presence of flotation reagents that would otherwise be capable of floating both cassiterite and silicate gan'gue.

2. The method of claim 1 wherein said aqueous pulp of ore' is obtained as a tailing product when sulfide minerals in a low grade Bolivian tin are floated from said ore.

3. In a method for recovering cassiterite from an aqueous ore pulp containing silicate and quartz gangue minerals wherein the ca ssiterite is floated from gangue in an acid circuit in the presence of a combination of a fatty acid and a water-dispersible fatty acid alkanolamide obtained by condensing 1 mol of fatty acid containing 12 to 18 carbon atoms with from 1 to 2 mols of an alkanolamine containing from 2 to 3 carbon atoms in an alkyl group,

the improvement which comprises a preliminary step of first subjecting said ore pulp to flotation in an acid circuit in the presence of said fatty acid alkanolamide and fluoride ion in the absence of free fatty acid, thereby producing a silicate-rich froth product and a machine discharge product which is a rough concentrate of cassiterite, and washing said machine discharge product with Water until it is substantially free from fluoride ions, thereby providing an aqueous pulp from which cassiterite can be floated from gangue minerals in an acid circuit in the presence of TABLE V.--FLOTATION OF CASSITERITE FROM MINUS 325 MESH GRINDING SLIMES 1 Calculated.

2 Iulp conditioned with HF for 5 minutes before adding Monamid 150-CE.

Data in Table V show that slimed cassiterite concentrates having grades appreciably in excess of 40% could be obtained only when the sliined pulp was prepared for silicate flotation with alkanolamide reagent in combination with hydrofluoric acid, either as hydrofluoric acid or by reaction of sodium fluoride with sulfuric acid to form hydrofluoric acid in situ. These data therefore show that the use of fluoride ion was essential in the silicate flotation step. comparison of the result of Test 17 with the result of Test 15 shows a considerable imsaid combination of fatty acid and fatty acid alkanolamide.

4. The method of claim 2 wherein said aqueous pulp is obtained as a machine discharge product when sulfide minerals in a low grade tin ore are floated from said ore.

5. In a method for concentrating cassiterite from an ore containing silicate and quartz gangue minerals, wherein an aqueous acidic pulp of the ore is conditioned for flotation of icassiterite with the combination of (1) a water-dispersible fatty acid alkanolamide obtained by condensing 1 mol of higher fatty acid containing 12 to 18 carbon atoms with from '1 to 2 mols of an alkanolamine containing 2 to 3 carbon atoms in an alkyl group and (2) lauric acid, and the pulp thus conditioned is subjected to froth flotation in an acid circuit, producing a [froth product which is a concentrate of cassiterite and a tailing which is a concentrate of gangue minerals,

a method for improving the grade of cassiterite in said froth product which comprises:

before conditioning said pulp with said combination'of fatty acid alkanolamide and lauric acid to float cassiterite, conditioning said pulp for flotation of silicate gangue minerals with fluoride ion and a cationic nitrogenous reagent selected from the group consisting of a water-dispersible salt of a fatty acid'amine containing 18 carbon atomsand a water-dispersible fatty acid alkanolamide obtained by condensing 1 mol of fatty acid containing 12 to 18 carbon atoms with from 1 to 2 mols of an alkanolamine containing from 2 to 3 carbon atoms in an alkyl group, and, without addition of fatty acid collector reagent to said pulp, subjecting the pulp to froth flotation in an acid circuit, thereby producing a froth product which is a concentrate of silicate gangue minerals and a machine discharge which is a rough concentrate of cassiterite, washing said machine discharge product to eliminate fluoride ion and slime therefrom and utilizing the resulting washed machine'discharge' product as feed for flotation of cassiterite with said combination of fatty [acid alkanolamide and fatty acid.

6.111 a method for concentrating cassiterite from an ore containing silicate and quartz gangue minerals wherein the cassiterite is selectively floated from gangue by conditioning an aqueous acidic pulp of said ore for flotation of cassiterite with the combination of lauric acid and a water-dispersib1e fatty acid alkanolamide obtained by condensing 1 mol of higher fatty acid containing 12 to 18 carbon atoms with from 1 to 2 mols of an alkanolamine containing 2 to 3 carbon atoms in an alkyl group, and the pulp thus conditioned is subjected to froth flotation in an acid circuit, producing a froth product which is a concentrate of cassiterite and a tailing which is a concentrate of gangue minerals,

the improvement which comprises:

before conditioning said pulp for flotation of cassiterite, incorporating fluoride ion and a waterdispersible fatty acid alkanolamide into said pulp without addition of a fatty acid collector reagent, said alkanolamide having been obtained by condensing 1 mol of higher fatty acid containing 12 to 18 carbon atoms with from 1 to 2 mols of an alkanolamine containing 2 to 3 carbon atoms in the alkyl group, and subjecting the pulp to froth flotation in an acid circuit, thereby producing a froth product which is a concentrate of silicate gangue minerals and a machine discharge which is a rough concentrate of cassiterite, and washing said machine discharge product to eliminate fluoride ion and slimes therefrom, thereby producing a concentrate that is more amenable to subsequent concentration by flotation with said combination of lauric acid and water-dispersible alkanolamide.

7. The method of claim 6 wherein said fatty acid alkanolamide is obtained by condensing 1 mol of coconut fatty [acid with 1 mol of diethanolamine.

8. In a method for concentrating cassiterite from an ore containing silicate and quartz gangue minerals wherein an aqueous acidic pulp of said ore is conditioned with the combination of (1) a water-dispersible fatty acid alkanolamide obtained by condensing 1 mol of higher fatty acid containing 12 to 18 carbon atoms with froml to 2 mols of an alkanolamine containing 2 to 3 carbon atoms in an alkyl group and (2) lauric acid, and the pulp is subjected to froth flotation in an acid flotation circuit, producing a froth product which isa concentrate of cassiterite and a tailing which is a concentrate of gangue minerals,

the improvement which comprises:

before floating cassiterite from said pulp with said combination of reagents, floating silicate minerals from said pulp in the presence of fluoride ion and a water-dispersible salt of octadecylamine in the absence of a free fatty acid collector reagent, thereby producing a machine discharge which is a rough concentrate of cassiterite and quartz, and washing said machine discharge product to eliminate fluoride ion and slime there from, thereby producing a concentrate which is more responsive to selective flotation of cassit erite from quartz with said combination of fatty acid alkanolamide and lauric acid collector reagents.

9. 'The method of claim 8 wherein said amine salt is octadecylamine acetate.

10. The method of claim 8 wherein said amine salt is octadecylamine acetate and said fatty acid alkanolamideis obtained by condensing 1 mol of coconut fatty air with 1 mol of diethanolamine.

11. A process for recovering cassiterite from an aqueous pulp of a cassiterite ore containing oxidized gangue minerals including silicate minerals and quartz, which comprises:

incorporating hydrofluoric acid with said pulp, conditioning said pulp for flotation of silicate minerals with a nitrogenous collector reagent selected from the group consisting of a water-dispersible rfatty acid alkanolamide containing -'l2 to 18 carbon atoms and a water-dispersible salt of a n-primary fatty amine containing 18 carbon atoms, subjecting the pulp tov froth flotation in an acid circuit to produce a froth product which is a concentrate of silicate minerals and a machine discharge product which is a rough cassiterite concentrate, washing said machine discharge product with water to eliminate fluoride and slime therefrom, conditioning said washed machine discharge product for froth flotation of cassiterite with a water-dispersible fatty acid alkanolamide and with lauric acid and subjecting the pulp thus conditioned to froth flotation in an acid circuit, producing a froth product which is a concentrate of cassiterite and a tailing, said water-dispersible fatty acid alkanolamide being obtained by condensing 1 mol of a higher fatty acid containing 12 to 18 carbon atoms with from 1 to 2 mols of an alkanolamide containing from 2 to 3 carbon atoms in an alkyl group.

12. A method for concentrating cassiterite from a low grade tin ore containing sulfide minerals, silicate minerals and quartz as gangue which comprises:

forming an aqueous 'pulp of said ore,

conditioning said aqueous pulp for sulfide flotation with a xanthate collector reagent selective to sulfide minerals in said pulp, subjecting the pulp thus conditioned to froth flotation, thereby producing a froth product which is a concentrate of sulfide mineral in said ore and a machine discharge product which is a concentrate of nonsulfide minerals,

deslirning said machine discharge product, vconditioning said deslimed machine discharge product for flotation of silicate minerals and residual sulfide minerals with fluoride ion and a nitrogenous collector reagent selected from the group consisting of a water-dispersible salt of a fatty acid amine containing 18 carbon atoms and a water-dispersible fatty acid alkanolamide obtained by condensing 1 mol of fatty acid containing 12 to 18 carbon atoms with from 1 to 2 mols'of an alkanolamine containing from 2 to 3 carbons atoms in an alkyl group, said nitrogenous collector reagent being used without addition of anionic collector reagent, subjecting said pulp thus conditioned to froth flotation in an acid circuit, thereby producing a froth product which is a concentrate of residual sulfide minerals and silicate minerals originally in said ore and a machine discharge product which is a rough concentrate of cassiterite in said ore,

washing said rough concentrate to eliminate fluoride ion substantially completely and to remove slime therefrom,

conditioning a pulp of said washed machine discharge for flotation of cassiterite with a fatty acid alkanolamide obtained by condensing 1 mol of fatty acid containing 12 to 18 carbon atoms with from 1 to 2 mols of an alkanolamine containing from 2 to 3 carbon atoms and with laun'c acid while maintaining the pulp acidic and subjecting the pulp thus conditioned to froth flotation in an acid flotation circuit, thereby producing a froth product which is a concentrate of cassiterite and a machine discharge product which is a concentrate of gangue minerals in said rough concentrate.

13. The method of claim 12 wherein said nitrogenous collector for silicate minerals is an alkanolamide obtained by condensing coconut fatty acid with from 1 to 2 mols of diethanolamine.

14. The method of claim 12 wherein said nitrogenous collector rfor silicate minerals is octadecylamine acetate.

15. The method of claim 13 wherein said fatty acid alkanolamide that is used to float cassiterite has been obtained by condensing coconut fatty acid with from 1 to 2 mols of diethanolamine.

References Cited by the Examiner UNITED STATES PATENTS 2,000,350 5/ 1935 Patek 2091'66 2,173,909 9/ 1939 Kritchevsky 209166 2,381,662 8/1945 Gaudin 209-166 3,167,502 1/1965 Duke 209---] 67 3,182,798 5/1965 Duke 209166 HARRY B. THORNTON, Primary Examiner.

R. HALPER, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,286,837 November 22, 1966 Venancio Mercade et al.

hat error appears in the above numbered pat- It is hereby certified t that the said Letters Patent should read as ent requiring correction and corrected below.

Column 3, line 57, for "concentrate" column 5, line 12, for C read C amines 10, line 3, after "sulfide" insert a comma; columns 11 and 12,

TABLE'III, thirteenth column, line 9 thereof, for "10.2" read 1.02 column 13, TABLE V, se renth column, subheading, line 3 thereof, strike out "Sn Signed and sealed this 12th day of September 1967.

read concentrates column Attest:

ERNEST W. SWIDER EDWARDJ. BRENNER Commissioner of Patents Attcsting Officer 

1. IN A METHOD FOR RECOVERING CASSITERITE FROM AN ORE CONTAINING SILICATE AND QUARTZ MINERALS WHEREIN THE CASSITERITE IS FLOATED FROM GANGUE MINERALS IN AN ACID PULP IN THE PRESENCE OF COLLECTOR REAGENTS CAPABLE OF FLOATING BOTH CASSITERITE AND SILICATE GANGUE MINERALS, A PRELIMINARY STEP OF SUBJECTING AN AQUEOUS PULP OF THE ORE TO FLOTATION IN AN ACID CIRCUIT IN THE PRESENCE OF A CATIONIC NITROGENOUS OF A FATTY ACID REAGENT, SAID CATION IN THE ABSENCE OF A FATTY ACID REAGENT, SAID CATIONIC NITROGENOUS COLLECTOR REAGENT BEING SELECTED FROM THE GROUP CONSISTING OF FATTY AMINE CONTAINING 18 CARBON ATOMS AND FATTY ACID AKANOLAMIDE DERIVED FROM FATTY ACIDS CONTAINING FROM 12 TO 18 CARBON ATOMS, THEREBY TO PRODUCE A SILICATE-RICH FROTH PROUCT AND A MACHINE DISCHARGE PRODUCT, WASHING SAID MACHINE DISCHARGE PRODUCT UNTIL SAID MACHINE DISCHARGE PRODUCT IS SUBSTANTIALLY FREE OF FLUORIDE ION, THEREBY PROVIDING AN AQUEOUS PULP THAT IS MORE AMENABLE TO SUBSEQUENT CONCENTRATION OF CASSITERITE BY FROTH FLOTATION IN AN ACID CIRCUIT IN THE PRESENCE OF FLOTATION REAGENTS THAT WOULD OTHERWISE BE CAPABLE OF FLOATING BOTH CASSITERITE AND SILICATE GANGUE. 